package com.objcat.playground.hdoj.hdoj1001;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int a = sc.nextInt();
            int result = 0;
            for (int i = 1; i <= a; i++) {
                result += i;
            }
            System.out.println(result + "\n\n");
        }
    }
}
